Hot isostatic presses are used in producing different types of articles, such as turbine blades for aircraft or artificial hip joints for implantation into persons. The press usually comprises a furnace provided with electric heating elements for increasing the temperature in the furnace chamber where the load, i.e. the articles, is being pressed in a loading space. After a finished pressing operation it is often important to rapidly cool the loading space so that the load therein will obtain the desired properties and so that grain growth is avoided or minimized. Furthermore, rapid cooling results in increased productivity since the load may be removed rapidly, thereby reducing the cycle time. However, it is also important that an even cooling throughout the loading space is achieved.
There have been attempts for cooling the loading space and the furnace chamber by injection of a cold gas directly into the loading space. Even though rapid cooling is obtained through this method, the disadvantage is that the load will become unevenly cooled, since gas that is substantially cooler than the gas in the loading space will flow through the load. This may lead to an uneven quality of the load and may even result in crack formation.
U.S. Pat. No. 5,123,832 discloses a hot isostatic press for achieving a more even cooling of the load, wherein a gas mixture is achieved by mixing, in an ejector, cold gas with hot gas from the furnace chamber. The temperature of the gas mixture which is ejected into the loading space is about 10% lower than the present temperature in loading space. The mixing of the cold gas and the hot gas in the ejector, requires a considerable throttling or restriction for providing a good mixing effect. The inlet for the mixed gas into the loading space is thus very small, typically 100 mm in diameter, whereas the diameter of the loading space is typically about 1.2 m. Even though a satisfactory cooling may be achieved, this construction also has drawbacks. During the pressing operation, when the furnace chamber is to be heated, the heating of the furnace chamber, and the loading space in particular, would become extremely uneven because of the small inlet area to the loading space, unless heating elements are provided on the side of the furnace chamber. In many cases it is desirable to only have heating elements at the bottom portion of the furnace chamber, for, inter alia, reasons such as simplicity and cost-saving. Thus, there remains a need for a simple alternative which provides good mixing and which does not have the above constructional limitations.